Progressive changes in the physical properties of polymeric compositions occur on aging as a result of the combined effects of heat, light, oxygen and ozone. Oxygen and ozone are the agents which are primarily responsible for deterioration of such polymeric compositions and such deterioration is generally referred to as thermal oxidation. It has been shown that an uncured polymer subjected to thermal oxidation first undergoes softening but as the extent of oxidation increases, it gradually becomes harder until a brittle material is finally formed. The tendency toward hardening as aging proceeds, observed in the later stage with an uncured polymer, is observed during the aging of cured polymers, as evidenced by a progressive rise in the modulus.
Antioxidants have been employed to minimize the deteriorating effects of oxidation on polymers. Because of the volatility and relative insolubility of many antioxidants in polymer compositions, only a small portion of the antioxidant added to the polymer system actually remains in the final polymer. It is, therefore, desirable to provide highly efficient, relatively non-fugitive antioxidants which impart a high degree of stability to polymers.